| The number of patients with heart failure is increasing year by year in the world.Heart transplantation is still the best treatment for patients with advanced heart failure.However,the serious shortage of heart donors promotes the application and development of mechanical circulation support devices in clinical practice.Aiming at the problems of long-term continuous constant flow pump lacking physiology,causing complications and affecting patients' life and health,this paper focuses on how to realize and enhance the blood flow pulsatility and improve the left ventricular assist device physiology.Firstly,the hemodynamic model of the cardiovascular coupling system is established.Few studies have considered including baroreflex regulation in cardiovascular system model,and the baroreflex models that have been added only simulate heart failure by changing ventricular characteristics or vascular resistance parameters of systemic circulation.In this paper,the cardiovascular lumped parameter model and the pressure baroreflex model can reproduce the hemodynamic characteristics of the normal and heart failure conditions,and the numerical simulation verifies the accuracy of the model.On this basis,coupled with the CFLVAD model,it can be used to simulate the hemodynamic characteristics of centrifugal pump or axial flow pump under different support degrees,which provides a numerical simulation platform for pulsatile varying speed and physiological control.Secondly,the effects of CFLVAD on pulsatility and ventricular unloading and hemodynamic characteristics are studied by hemodynamic model of the cardiovascular coupling.The square wave,sinusoidal wave and triangular are studied as variable speed control sources.Also,the amplitude,frequency and phase of each waveform are changed to modulate a variety of different variable speed control modes,and the simulation experiment is carried out on the established simulation platform of the hemodynamic model of cardiovascular coupling system.In this paper,two control modes of the same frequency with the natural heart rate(called synchronous modulation)and different with the natural heart rate(called asynchronous modulation)are studied respectively.The results show that square pulsatile varying speed control is conducive to improve the blood flow pulsatility;increasing the amplitude can effectively improve the blood flow pulsatility,but increasing the amplitude too much will lead to pump regurgitation;both synchronous and asynchronous control can enhance blood flow pulsatility and allow a certain degree of ventricular unloading;in the asynchronous control mode,when the pulsatile duty cycle is 50%,the blood flow pulsation can be improved to the greatest extent,but low frequency is more likely to enhance blood flow pulsatility;synchronous pulsatile varying speed control provides more physiological hemodynamics;synchronous copulsation control is beneficial to improve blood flow pulsation and synchronous counterpulsation control is beneficial to ventricular unloading.It provides a theoretical basis for the realization of ideal pulsation.Thirdly,a pulsatile verying speed controller is developed and a in-vitro simulation platform is built to achieve a high pulsatile flow with the pulse pressure of 56 mmHg at the modulation frequency of 30 bpm.In addition,the experiment verifies the validity of the theoretical study on the influence of modulation frequency and modulation amplitude on blood flow pulsatility.The lower the modulation frequency,the better the blood flow pulsatility;the greater the amplitude,the better the blood flow pulsatility,but the actual maximum amplitude of pump speed will be limited by the modulation frequency.Fourthly,a multi-objective physiological control system is designed,and physiological feedback variables can be obtained by model estimation to avoid instability and insecurity after sensor implantation.A hierarchical control strategy is proposed to solve the conflict control problem among suction prevention control,regurgitation prevention control and adaptive adjustment of blood flow pulsatility.The simulation results show that the multi-objective physiological control can adapt to any changes in ventricular load,and can adaptively adjust the pump flow rate to provide adequate physiological perfusion and enhance the blood flow pulsatility in the diseased cardiovascular system without the ventricular suction and pump regurgitation.The system improves the physiology of CFLVAD.The established hemodynamic model of the cardiovascular coupling system in this paper provides a numerical simulation experimental platform for CFLVAD pulsatile varying speed control and physiological control.On this platform,the research under various conditions and multiple pulsatile varying speed control modes has laid a theoretical foundation for the realization of pulsation control.The developed pulsatile varying speed controller and in-vitro simulation platform achieve ideal blood flow pulsatility.The multi-objective physiological control system with hierarchical control strategy further improved the physiology of CFLVAD. |
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